1. Field of the Invention
The invention relates to a consolidant and to its use for producing hydrolytically and hydrothermally stable molded articles and coatings, and to the products formed therefrom.
2. Discussion of Background Information
Binders are of high significance especially for the binding of compact or particulate products in order to produce moldings therefrom. A particular problem in this context is the hydrolysis stability of consolidants when they are exposed to aggressive conditions. This is because, for an efficient use of binders, it is important that the stability is maintained for as long as possible even under aggressive conditions such as high pressures, high temperatures, contact with aqueous or corrosive media such as acids or bases, and the bond strength must not be reduced significantly. In this regard, organic polymers as binders are frequently of inadequate stability.
The production of composite materials from particulate systems with suitable binders is also difficult when the composite materials are to lose only a little porosity compared to the binder-free product. For example, it is possible with organic polymer binders to produce porous composites, but it is found that it is barely possible to maintain the original porosity. In the case of reduced binder use, it is possible to produce porous systems, but such composites are unsuitable for many applications, especially at elevated temperatures and in the environment of organic liquids owing to the property of the organic polymers to swell up or go into solution in the presence of organic solvents.
The use of purely inorganic binders which are obtainable, for example, via the sol-gel process does lead to a bond in which an appropriate porosity is maintained in the consolidated molding body, but the bonded system is very brittle, fragile and not sufficiently resistant to mechanical stresses such as shear stresses or high pressure stresses.
Moreover, it is frequently appropriate to produce moldings under the conditions under which they are also employed later. It is therefore frequently desirable to cure the consolidated moldings under an elevated pressure. This is completely impossible for many consolidants.
It was an object of the invention to provide a process for producing consolidated moldings and coatings which are in particular hydrolysis-stable and hydrothermally stable even under corrosive conditions. Retention of a desired porosity should also be possible. Moreover, a good bond strength with sufficient flexibility should be achieved. It was also desired to enable consolidation under hydrothermal conditions, i.e. under elevated pressure and elevated temperature.
The object is achieved by the provision of a consolidant for producing hydrolysis-stable molding bodies or coatings, comprising a hydrolyzate or precondensate of    (a) at least one organosilane of the general formula (I)RnSiX4-n  (I)     in which the R radicals are the same or different and are groups not eliminable by hydrolysis, the X radicals are the same or different and are groups eliminable by hydrolysis or hydroxyl groups, and n is 1, 2 or 3,    (b) at least one hydrolyzable silane of the general formula (II)SiX4  (II)     in which the X radicals are each as defined above; and    (c) at least one metal compound of the general formula (III)MXa  (III)     in which M is a metal of main groups I to VIII or of transition groups II to VIII of the Periodic Table of the Elements including boron, X is as defined in formula (I), where two X groups may be replaced by one, oxo group, and a corresponds to the valency of the element; where the molar ratio of silicon compounds used to metal compounds used is in the range from 10 000:1 to 10:1.